Hey hi,There is slight infection also persistent pain after multiple Re-RCTs, despite normal X-rays and CBCT, can be quite complex. It could be due to a micro-fracture , or even non-dental causes like referred nerve pain (neuralgia) or sinus issues
Next Steps
Please consult an Endodontist (Root Canal Specialist) for a microscopic evaluation. If the tooth structure is compromised after 3 retreatments, you may need to consider an Apicoectomy or, in the worst case, extraction followed by an implant to finally end the pain.